We have shown in two publications that magnetic circular dichroism (MCD) is a valuable technique for: the quantitative determination of the three cytochromes (P-450, P-420, and b5) present in liver microsomes with a single measurement; the determination of the extent of induction of a P-450 by an inducer; the determination of different cytochromes (P-450 and P-448) arising from pretreatment with different inducers; and the determination of substrate binding and spin-state change from room-temperature measurements. As a result of further work we can now solubilize, separate, and purify two forms of P-450. Preliminary MCD spectra reveal distinct differences between the two forms and indicate that MCD will be very useful for characterizing P-450's. We propose an in depth investigation of the MCD of cytochromes P-450. This involves work in several areas: (a) Fundamental spectral studies on the purified forms of P-450 induced by phenobarbital, 3-methylcholanthrene and beta-naphthoflavone; on these forms ligated with CO, NO, CN and EtSCN; on their interaction with substrates like benzphetamine; on the oxygenated intermediate; and on some product adduct intermediates; (b) Comparison of the spectra of P-450 with several synthetic model compounds; and (c) Applications to P-450 in the lung, adrenal cortex and in cancer cells. In addition, combined MCD and metabolism studies on several purified forms of P-450 will be made using carcinogen 2-Acetylaminofluorene and a series of halocarbon compounds. We will also reconstitute a purified P-450 into a well-defined phospholipid bilayer using a special dialysis procedure. We also propose to continue work on several projects. These are: (a) Calculations on the MCD of purines; (b) The MCD of dinucleotide analogs; (c) An MCD and Shpol'skii spectral study of some metalloporphyrins; and (d) The MCD of abnormal hemoglobins.